Spring rate selection

eric widen

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Maybe I can get a little direction from some of you. I have a 4 seat buggy that is new to me and I am looking for help with rear spring rates and maybe some valving direction. The motor is a Chevy 4.3 rear engine with a Mendeola 2d, a 15 gallon full cell and 35” spare.
I installed new 14” fox 2.5 factory coilovers and i will be buying new 16” fox 3-tube bypasses soon. I currently have 16” 450 lb over 16” 600 lb springs on the rear for a combined rate of 257 lbs. These are not new springs and they have been on the car for a while. I measured the spring at full droop with the Pre-Load ring only hand tight if that at 32”. I then set the car down and measured the coils to be 26.5. According to my math this gives me a corner weight of roughly 1415 lbs. Spring rate seems to heavy to me as I do not have any room to add Pre-Load to maintain a 40% droop. Pivot to coilover distance is 14”, pivot to center line of wheel is 25” and pivot to bypass is 20”.
I was thinking if i run 350 over 450 it would give me a combined rate of 197 lbs which would equal 7.18” of droop on the shock and allow for 1.58” of Pre-Load to sit at 40% droop at tide height. Does this sound correct? Hopefully my math is not fubar. Also anyone have any direction for valving on the coilover and bypass? I was gonna use the lightest shim stack fox offers.
The terrain i am normally driving in is barstow, Johnson Valley, and Ocotillo.
 
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biggjim

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Fox generally does a 50/50 valving on a coil over when combined with a bypass. You would have to look at a chart to figure out what shims are use. Mine happened to be a .010 stack compression and rebound. I would think you would want a fairly heavy compression stack for the rear of a buggy in the bypass shock. As far as springs anyone you talk to is going to want corner scale weights to help with springs.
 

Goatpoker

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Maybe I can get a little direction from some of you. I have a 4 seat buggy that is new to me and I am looking for help with rear spring rates and maybe some valving direction. The motor is a Chevy 4.3 rear engine with a Mendeola 2d, a 15 gallon full cell and 35” spare.
I installed new 14” fox 2.5 factory coilovers and i will be buying new 16” fox 3-tube bypasses soon. I currently have 16” 450 lb over 16” 600 lb springs on the rear for a combined rate of 257 lbs. These are not new springs and they have been on the car for a while. I measured the spring at full droop with the Pre-Load ring only hand tight if that at 32”. I then set the car down and measured the coils to be 26.5. According to my math this gives me a corner weight of roughly 1415 lbs. Spring rate seems to heavy to me as I do not have any room to add Pre-Load to maintain a 40% droop. Pivot to coilover distance is 14”, pivot to center line of wheel is 25” and pivot to bypass is 20”.
I was thinking if i run 350 over 450 it would give me a combined rate of 197 lbs which would equal 7.18” of droop on the shock and allow for 1.58” of Pre-Load to sit at 40% droop at tide height. Does this sound correct? Hopefully my math is not fubar. Also anyone have any direction for valving on the coilover and bypass? I was gonna use the lightest shim stack fox offers.
The terrain i am normally driving in is barstow, Johnson Valley, and Ocotillo.
Math seems pretty good. You also get some spring effect from the nitrogen charge in the two shocks. Driving style has an impact too, if you plan to bomb it you might want more spring than the 2" preload rule.

With Fox bypasses you have more bleed than kings so that will help. 10's ion both rebound and compression the coil will be fine. Again, depending on driving style and "oh poop" control, 15 or 20's in the bypass on compression. 12's for rebound


Sent from my iPad using race-deZert mobile app
 

*TRD*

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You have all the right ideas regarding how to measure your setup. You want less split on spring rate than you have now.

Everyone has different ideas for how to tune ... some are better than others.
 

eric widen

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I picked up 400 over 450 springs and put new bypasses on the car. I kept the off-the-shelf valving to try out and get a base line and go from there. Now i am trying to determine what droop vs bump ratio. Ride height is not really a determining factor for me but rather the suspension working the best it can. I set the car with two inches of preload and i am at about 19” to bottom of frame and there is about 10.5” of shaft showing which leaves 5.5 inside the bypass. This is a 65/35% bump to droop respectively. I notice most other cars similar to mine (desert dynamics type of dual sport car) have the majority of the bypass shaft showing. Think i should add a little more preload? I was thinking roughly another 1/4”. Correct me if I’m wrong. This type of car should be at 1/3 droop 2/3 bump unlike a linked truck that should be more like 50/50.
 

partybarge_pilot

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2" of preload is more than I would run. Picture of the rear suspension? If it's really like a DD car, the shocks are probably way past 90* at full bump. Falling ratio is bad for spring rate and valving.
 

eric widen

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I was under the impression that 2-3” for preload in the rear was what should be achieved. I will try to post some pics. I also have about 3 inches of ground clearance at full bump.
 
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eric widen

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I know it doesn’t look like a dd car. it was built by foddrill but most people are not familiar with foddrill cars like this and a dd car is the most similar as they have the same basic design of front suspension and shock layout(vs alumicraft which is different).
 

BDR LOVES BAJA

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Maybe I can get a little direction from some of you. I have a 4 seat buggy that is new to me and I am looking for help with rear spring rates and maybe some valving direction. The motor is a Chevy 4.3 rear engine with a Mendeola 2d, a 15 gallon full cell and 35” spare.
I installed new 14” fox 2.5 factory coilovers and i will be buying new 16” fox 3-tube bypasses soon. I currently have 16” 450 lb over 16” 600 lb springs on the rear for a combined rate of 257 lbs. These are not new springs and they have been on the car for a while. I measured the spring at full droop with the Pre-Load ring only hand tight if that at 32”. I then set the car down and measured the coils to be 26.5. According to my math this gives me a corner weight of roughly 1415 lbs. Spring rate seems to heavy to me as I do not have any room to add Pre-Load to maintain a 40% droop. Pivot to coilover distance is 14”, pivot to center line of wheel is 25” and pivot to bypass is 20”.
I was thinking if i run 350 over 450 it would give me a combined rate of 197 lbs which would equal 7.18” of droop on the shock and allow for 1.58” of Pre-Load to sit at 40% droop at tide height. Does this sound correct? Hopefully my math is not fubar. Also anyone have any direction for valving on the coilover and bypass? I was gonna use the lightest shim stack fox offers.
The terrain i am normally driving in is barstow, Johnson Valley, and Ocotillo.
What formulas did you use to be able to get all that info?
 

michael.gonzalez

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1/[(1/k1)+(1/k2)]= keq

k1 = spring rate 1
k2 = spring rate 2
keq = combined equivalent spring rate
 
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